W.H.O.

...........Where caries risk is high or increasing authorities may consider addition of fluoride to the demineralized public water supply up to in the range of the WHO GDWQ level of 1.5 mg/l,preferably adjusted to water consumption rates; however, other factors must also be considered.For example, in countries such as those in Scandinavia, where public dental awareness is very high and alternative vehicles for fluoride (e.g. fluoridated toothpaste) are widely available and widely used, a decision to not fluoridate the water, or remove fluoride, or to supply drinking
water with suboptimal levels of fluoride would likely be of little consequence. On the other hand in developing and developed countries where public dental health awareness in some population groups (e.g. lower income) might be much lower, water containing either natural or added fluoride at concentrations of 0.5 to1.0 mg/l would be important for dental health.........